• CYP3A4;
  • Alcohol;
  • Protease Inhibitors;
  • Spectral Binding;
  • Inhibition

Background:  Cytochrome P450 3A4 (CYP3A4) is the most abundant CYP enzyme in the liver, which metabolizes approximately 50% of the marketed drugs including antiretroviral agents. CYP3A4 induction by ethanol and its impact on drug metabolism and toxicity is known. However, CYP3A4–ethanol physical interaction and its impact on drug binding, inhibition, or metabolism is not known, except that we have recently shown that ethanol facilitates the binding of a protease inhibitor (PI), nelfinavir, with CYP3A4. The current study was designed to examine the effect of ethanol on spectral binding and inhibition of CYP3A4 with all currently used PIs that differ in physicochemical properties.

Methods:  We performed type I and type II spectral binding with CYP3A4 at 0 and 20 mM ethanol and varying PIs’ concentrations. We also performed CYP3A4 inhibition using 7-benzyloxy-4-trifluoromethylcoumarin substrate and NADPH at varying concentrations of PIs and ethanol.

Results:  Atazanavir, lopinavir, saquinavir, and tipranavir showed type I spectral binding, whereas indinavir and ritonavir showed type II. However, amprenavir and darunavir did not show spectral binding with CYP3A4. Ethanol at 20 mM decreased the maximum spectral change (δAmax) with type I lopinavir and saquinavir, but it did not alter δAmax with other PIs. Ethanol did not alter spectral binding affinity (KD) and inhibition constant (IC50) of type I PIs. However, ethanol significantly decreased the IC50 of type II PIs, indinavir and ritonavir, and markedly increased the IC50 of amprenavir and darunavir.

Conclusions:  Overall, our results suggest that ethanol differentially alters the binding and inhibition of CYP3A4 with the PIs that have different physicochemical properties. This study has clinical relevance because alcohol has been shown to alter the response to antiretroviral drugs, including PIs, in HIV-1-infected individuals.